Here is my 2 cents. In the way it worked before c24 with was 3/4 with pre-PR credit, the credit was never limited to just the 4 years as that wouldn't really make sense because there would be no need to limit the credit to a year because the maximum you could get then would be a year anyway.
So unless this new 3/5 rule is explicitly changing that, then you will be able to count ANY time spent as a worker/student/refugee towards citizenship, not just the last 5 years. In fact, since it's not explicitly written in the law that the pre-PR credit is limited to the 5 year period, it makes it open to challenge. So I'm 99.9% sure that there isn't that limit.
I'll go dig into the wording of the pre C-24 act to find the wording if I have time.